In Third Generation (3G) communication systems, Dynamic Link Adaptation (DLA) is used to compensate for degraded radio propagation conditions that would require the User Equipment (UE) to transmit at a transmission power greater then the maximum allowed, or physical maximum, transmission power. Transmissions that require to be transmitted at a power level greater than the maximum power level are transmitted at the maximum power level in 3G communication systems. When these signals are transmitted at the maximum power level (which is less than their desired transmit power level) they experience degraded performance and have increased error rates, increasing the likelihood that the transmitted data will not be received, and that the system resources being used are being wasted.
One prior art method for handling this maximum power condition is to continue the transmission at the maximum allowed or physical maximum transmission power and rely on the error correction capabilities of the receiver to correct any errors that may occur. This ultimately results in undesirable system performance, since the transmission will be made at a power level that is not adequate to maintain the desired level of error rate performance.
Another method for dealing with the maximum power condition is to reduce the Uplink (UL) data requirement for the period that the required transmission power to maintain the desired level of error rate performance is greater than the maximum power capability. This method maintains the desired error rate performance by the reduction of the data rate.
It is also possible to continue UL transmissions when the desired power would exceed the maximum power capability without effecting the UL data requirement by allowing the Block Error Rate (BLER) to increase. This effect is considered to be unavoidable for the period from when the maximum power condition is perceived to when the UL transmissions can be reconfigured to a reduced overall rate. In 3G wireless standards, UE performance requirements are specified that limit this period.
There is strong motivation to exceed the specified requirements since transmissions that require a power level greater than the maximum transmit power level are likely to fail. Services that allow for data retransmission of failed transmissions result in increased overhead, reduced radio resource efficiency and reduced UE battery life. Services that do not allow for retransmission result in an increase in the BLER, thereby causing subsequent increased power requests to attempt to maintain the BLER quality target. Since the UE is already transmitting at its maximum power, an increase in signal to interference ratio SIR target used in the UL transmit power control algorithm does not improve the BLER performance for the current channel conditions. If the channel conditions improve, the increased SIR target will require the UE to transmit at a power level greater than necessary to maintain the desired performance, resulting in reduced radio resource efficiency and battery life.
To achieve or exceed the performance requirements for improved Quality of Service (QoS), an efficient method of adjusting the UL transmission requirements is necessary.
In 3G communication systems, individual data streams are assigned to Transport Channels (TrCHs) with specific QoS capabilities, which are configured to achieve specified BLER quality targets. The physical channel(s) assigned to the UE support multiple TrCHs simultaneously; this is called a Coded Composite Transport Channel (CCTrCH). The CCTrCH allows for varying amounts of data on each TrCH to exist in any specific Transmission Time Interval (TTI). The TTI period is specific to each TrCH. Within each TTI period for a specific TrCH, the amount of data transmitted is specified by a Transport Format (TF).
For the CCTrCH in any specific TTI period, the set of TFs for each TrCH is known as the Transport Format Combination (TFC). The set of all of the available TFCs, (i.e. all of the available allowed multiplexing options), is known as the Transport Format Combination Set (TFCS).
For each UL CCTrCH, the UE Medium Access Control (MAC) entity selects a TFC for transmission on a TTI basis. This TFC and associated data is provided to the physical layer for transmission in the physical data request primitive. If the physical layer subsequently determines transmission of this TFC exceeds the maximum or allowable UE transmission power, a physical status indication primitive is generated to the MAC to indicate that maximum power or allowable transmission power has been reached.
When the MAC is informed of the maximum or allowable transmission power has been reached, the TFCs that would cause this condition to continue to exist are blocked, that is, removed from the set of available TFCs, unless the TFC is one of the TFCs which according to the 3GPP standards cannot be blocked. Blocked TFCs may be later restored to the set of available TFCs by unblocking them in subsequent periods when the UE transmission power measurements indicate the ability to support these TFCs with less than or equal to the maximum or allowed UE transmission power.
There are, however serious drawbacks with the current manner in which TFCs are removed. As aforementioned, the physical layer determines whether the transmission of a TFC would require exceeding the maximum or allowable UE transmission power, and then a physical status indication primitive is generated to the MAC entity that indicates maximum power or allowable power has been reached. Using this method, the UE could be in the maximum power state for approximately 60 milliseconds or more while the MAC reconfigures the set of available TFCs to remove the blocked TFCs and start selecting TFCs from the updated set of available TFCs. The UE will reduce the available TFCs only to the power requirement for the TFC that exceeded the transmission power capability. The UE will then likely choose the TFC with the next lower transmission power requirement. However, there is no guarantee that the reduced set of TFCs will not require power in excess of the maximum power. This results in another iteration of the process, and an additional delay, to further reduce the set of TFCs. For each TFC that is eliminated, data and radio resources are lost for the given TTIs. Ultimately, the performance of the system is degraded during the maximum power condition.
Additional performance concerns arise when the UE is attempting to recover the TFCs that have been blocked due to the maximum power condition. It is desirable to unblock, (i.e., recover), TFCs as quickly as possible to have a more complete set of TFCs available for the UE to use. Ultimately, the performance of the system is improved when the TFCs are recovered efficiently.
Accordingly, the prior art methods of handling the situation where the UE is in its maximum power state fall far short of acceptable system performance. It would be desirable to have an improved method of expeditiously reducing the set of TFCs for the duration when maximum UE power condition is achieved, and expeditiously restoring the TFCs when the maximum UE power condition has passed.